Back in the day, there was a very bad association with the superhero movie. Superheroes were for kids, and so those movies were made for a kid audience. Cheap costumes, horrid dialogue, and clichéd stories. Anyone over the age of 12 would groan and shuffle away as quickly as possible.
I'm thinking this changed back in 1989. We got Michael Keaton as Bruce Wayne/Batman in a movie, that while it did have its campy moments, was not a kids film. There was an attempt after that to increase the adult level of superhero films. Not all of them succeeded. Dolph Lundgren as the Punisher, also in 1989 comes to mind. Captain America in 1990. Then in 1998, Blade came along. A heavy R rated film with plenty of stuff not aimed for kids, and a reasonable success, spawning two sequels. Now you can't go anywhere near a theatre or TV without hearing news on the latest Marvel Cinematic Universe pic, or similar plans from Warner Brothers/DC with Batman vs. Superman or Justice League.
And while I love what has been done in comic adaptations, especially in the Marvel films, I have to wonder, is the public going to get burned out on them. This year we've got Captain America - The Winter Soldier and Guardians Of The Galaxy. Batman vs. Superman is reportedly going to go head to head with The Avengers - Age of Ultron. Is there going to be a time when people go 'great, another comic book movie coming out'. And they may be great films, but no one will care. That's my fear.